Help with Snippet/paint.

[Resistance]

I'm making a type of "Snippet" program that takes a screenshot of your, well screen obviously. Right now I have a capture, clear, and save button.
After the screenshot is captured I want to be able to Freehand draw on it but I can't seem to figure out how.
So far I have a small idea but I don't know what to do with it.
Underneath the public class-

Dim q As System.Drawing.Graphics

And in the picture box

Private Sub PictureBox1_MouseDown(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles PictureBox1.MouseDown
q.Draw....

But I don't know how to make it freehand on MouseDown.

What do you mean by "freehand", do you mean when the mouse it attempting to draw on the picture or when it has already drawn on the picture?